It’s been known for some time that one’s gastrointestinal tract functions in essence as one’s “second brain”, lined with hundreds of millions of neurons. In fact, the gut manufactures more dopamine and serotonin, important neurotransmitters that powerfully influence mood and motivation, than does the “head” brain.
The accepted view has been that due to the blood-brain barrier, hormones produced in one’s g-i tract can’t travel to the brain. Nevertheless, the gut can generate nerve signals that can communicate with the brain and thereby influence mood.
A recent study has shown that addition of probiotics to one’s diet can potentially lower anxiety and heightened reactivity to negative experiences.
Researchers at the David Geffen School of Medicine at UCLA found that women who consumed a fermented milk product with probiotics for four weeks experienced changes in brain areas that regulate emotional processing.
The women involved in the study were healthy, without any digestive or psychiatric disorders. One group of study subjects received the fermented milk product (FMPP), another group received a non-fermented milk product (control group), and a third group received no treatment (no intervention group).
The first two groups were directed to consume their assigned milk product (125 grams, or about ¼ cup) twice a day, for 28 days. All study subjects were given detailed brain scans (functional magnetic resonance imaging) before and after the four-week intervention, to gauge how their brains responded to an attention task. The emotional faces task involved viewing human faces and matching them to negative emotions such as anger and fear.
Such a task measures both instinctive and conscious brain reactions to emotion-laden information. In other words, the task can pick up on minute shifts in emotion regulation.
Lo and behold, the women in the FMPP group showed a reduction of activity in the key brain regions responsible for modulating emotions, as compared to the beginning of the study. The women who consumed the non-fermented milk product showed no change, and the women in the group that received no treatment actually increased in brain reactivity.
This is the first time that such changes in brain activity have been demonstrated in humans after probiotic consumption, although animal studies have shown alterations in pain and emotional responses after shifts in gut flora.
The fact that the women who consumed a non-fermented milk product did not exhibit a shift in brain activity indicates that the probiotics rather than the dairy were the key factors. This is important, due to the popular belief (in some circles) that the amino acid tryptophan, present in dairy products as well as other foods such as turkey, promotes feelings of calm, relaxation, and sleepiness. (Consider the advice frequently given to drink a warm glass of milk before bed.) In addition subjects were not told which milk product they were being given, and the non-fermented milk product and FMPP were identical in terms of appearance, consistency, flavor, calories, protein, and fat content.
In addition, four weeks is a relatively short period of time, especially when one takes into account that most anti-depressant medications take between four to six weeks to take effect. Also, approximately one cup of a fermented milk product a day is a reasonable amount to consume, and these days grocery store shelves are stocked with an enormous amount of options. So, if you’re struggling with anxiety or tension, heading to the nearest market and stocking up on some yogurt or kefir might be worth a try.
Tillisch, K., Labus, J., Kilpatrick, L., Jiang, Z., Stains, J., Ebrat, B., Guyonnet, D., Legrain-Raspaud, S., Trotin, B., Naliboff, B., & Mayer, E.A. (2013). Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology, 144(7), 1394-1401.